1) Field of the Invention
The present invention relates to a clamp an electronic assembly comprising connecting a power transistor to an underlying conducting layer. The clamp has a acting as a holder and heat sink and may also constitute an electromagnetic barrier between the input and output sides of the power transistor. It provides a solderless connections for the transistor base and collector to the underlying circuit board.
2) Discussion of Related Art
Many electronics applications use electronic components such as high power transistors which generate comparatively large amounts of heat. One such application is the radio frequency (RF) power amplifier at the output stage of a radio transceiver. Such a circuit element generates in a very limited area a substantial amount of heat as well as electromagnetic (EM) emission.
A solution to these problems is provided in our own co-pending U.S. patent application No. 08/640,256 (Myrberg) filed on 30 Apr. 1996 (corresponding to PCT SE97/00706, published on 7 Nov. 1997. It describes a heat sink bridge between the two mounting/grounding flanges at the ends of the transistor, spanning the transistor and holding it in place on the circuit board by means of screws extending through respective ends of the bridge and respective mounting flanges. In addition to the mounting and heat sink functions it also acts as an electromagnetic barrier.
The base and collector tabs extending from the transistor transversely with respect to the mounting/grounding flanges have in this case hitherto been manually soldered or glued to the circuit board. As the power amplifier is frequently turned on and off for radio transmission there is a risk that these solder joints will crack as the different materials expand and contract due to temperature variations. Cyclic shear stresses are induced in the solder joints due to the different heat expansion coefficients of the circuit board and the transistor package.
It is known by inter alia U.S. Pat. No. 4,597,617 and U.S. Pat. No. 5,099,393 to mount an integrated circuit on a circuited substrate by using pressure pads to establish and maintain contact between the conducting parts of the IC and the substrate. These two references do not relate to the mounting of power transistors and the problems of thermic stress associated therewith.